1. Field of the Invention
The present invention generally relates to an anti-thief security sensor assembly and, more particularly, to the anti-thief security sensor assembly of a type wherein while an infrared beam emitted from an infrared beam projecting unit is constantly received by an infrared beam receiving unit, an alarm is generated when an unauthorized intruder traverses across the path of travel of the infrared beam from the infrared beam projecting unit towards the infrared beam receiving unit.
2. Description of the Prior Art
The anti-thief security sensor assembly is known in which a beam projector of an infrared beam projecting unit and a beam receiver of an infrared beam receiving unit are installed at opposite ends of a rectilinear guard area spaced an appropriate distance from each other with their optical axes aligned with each other. The infrared beam receiving unit is so operated that when the receiver senses the infrared beam the receiver can output an electric signal of a signal level proportional to the amount of the infrared beam received. The electric signal so outputted is, after having been amplified by an amplifier circuit, processed by a detecting circuit to remove a disturbance light component and then to convert it into a signal of a level proportional to the received beam signal, and the signal level from the detecting circuit is subsequently determined by a signal discriminating circuit as to whether or not the level of the signal is lower than a predetermined detection level. In the event that the level of the received beam signal attains a value lower than the predetermined detection level as a result of the infrared beam from the beam projecting unit towards the beam receiving unit having been intercepted by traverse of an unauthorized intruder, the signal discriminating circuit outputs a detection signal with which an alarm generator is driven to output an alarm signal warning that the unauthorized intruder has entered the guard area.
The anti-thief security sensor assembly is generally capable of monitoring the guard area ranging from a rectilinearly close distance to a rectilinearly long distance of a few hundred meters, and the longer the rectilinear distance, the more difficult it is to install the beam projector and the beam receiver with their optical axes aligned with each other as accurately as possible at respective locations a distance from each other. Accordingly, the conventional anti-thief security sensor assembly includes a sighting instrument so as to facilitate the alignment of the respective optical axes of the beam projecting and receiving units. To align the respective optical axes of the beam projecting and receiving units with each other at the time of installation or servicing of the anti-thief security sensor assembly, a servicing worker has to look through a viewing hole of the sighting instrument mounted on the beam receiving unit to adjust the angle of orientation of the beam receiver in both vertical and horizontal directions to roughly align the respective optical axes of the beam projecting and receiving units with each other with naked eyes. Once this has been done, while the signal level proportional to the amount of the infrared beam received by the beam receiver is read out with the use of a level meter such as, for example, a voltmeter electrically connected with and built in the detecting circuit of the beam receiving unit, the angle of orientation of the beam receiver in the vertical and horizontal directions are finely adjusted to render the reading of the signal level to match with a predetermined level of the infrared beam that ought to be received, thereby completing the job of aligning the respective optical axes of the beam projecting and receiving units.
In recent years, the anti-thief security sensor assembly has come to be known in which the beam receiving unit is provided with a signal output means for outputting a level display signal descriptive of the amount of the infrared beam received to the beam projecting unit and, on the other hand, the beam projecting unit is provided with a receiving means for receiving the level display signal and a display means for displaying the level display signal so received. See, for example, the Japanese Laid-open Patent Publication No. 4-71099. According to this prior art anti-thief security sensor assembly, the fine alignment of the respective optical axes of the beam projecting and receiving units is carried out by manipulating the sighting instrument of the beam projecting unit while the display of the level display signal received from the receiving means is monitored with naked eyes. While the optical adjustment on the side of the beam projecting unit had required intervention of at least two servicing workers, assigned respectively to sites of installation of the beam projecting and receiving units, who were required to communicate wireless with each other as to the level of the infrared beam received, this prior art anti-thief security sensor assembly disclosed in the above referenced publication requires only one servicing worker to accomplish a similar optical adjustment.
According to the prior art, difficulty has been encountered that even when the level of the infrared beam being received by the beam receiving unit is desired to be ascertained, no transmission of the level display signal from the beam receiving unit to the beam projecting unit is possible. In other words, transmission of the level display signal from the beam receiving unit to the beam projecting unit is possible only when and after a receiver cover enclosing and protecting the beam receiving unit is physically opened and mere physical opening of a projector cover enclosing and protecting the beam projector does not allow the beam projecting unit to receive the level display signal transmitted from the beam receiving unit. Accordingly, unless those two covers for the beam receiving and projecting units are physically opened, no fine adjustment of the optical axis of the beam projector is possible.
In view of the above, it has hitherto been carried out for a servicing worker to first open the projector cover for the beam projecting unit, then to move to the site of installation of the beam receiving unit to open the receiver cover for the beam receiving unit so that the optical axis of the beam receiving unit can be adjusted in the manner described above, again to move to the site of installation of the beam projecting unit after the adjustment of the optical axis of the beam receiving unit to thereby effect the adjustment of the optical axis of the beam projecting unit, thereafter to return to the site of installation of the beam projecting unit to mount the once opened projector cover onto the beam projecting unit, and finally to again return to the site of installation of the beam receiving unit to mount the once opened receiver cover onto the beam receiving unit, thereby completing the alignment of the respective axes of the beam projecting and receiving units with each other. For this reason, the servicing worker has to make at least one round and half trip between the respective sites of installation of the beam projecting and receiving units. This is indeed a substantial burden on the servicing worker if the guard area extends a substantial distance, accompanied by a substantial length of time required to complete the optical axis alignment.
In view of the foregoing, the present invention is intended to provide an anti-thief security sensor assembly wherein only physical opening of a projector cover for a beam projecting unit is sufficient to achieve the adjustment of the optical axis of the beam projecting unit relative to that of a beam receiving unit.
In order to accomplish the foregoing object of the present invention, there is provided an anti-thief security sensor assembly including a beam projecting unit for projecting an infrared beam and a beam receiving unit for receiving the infrared beam projected by the beam projecting unit. The beam projecting unit includes a projector base having a sensor circuit mounted thereon and a projector cover detachably mounted on the base for enclosing and projecting the sensor circuit, an opening detecting switch for detecting a physical opening of the projector cover and a transmission request generating circuit operable in response to the detection of the physical opening of the projector cover by the opening detecting switch for outputting a received beam level transmission request signal to the beam receiving unit. The beam receiving unit is provided with a level output circuit operable in response to the received beam level transmission request signal to transmit to the beam projecting unit a level display signal indicative of the amount of the infrared beam received by the beam receiving unit.
With this anti-thief security sensor assembly according to the present invention, when the projector cover is physically opened at the time of installation or servicing of the anti-thief security sensor assembly, the opening detecting switch detects such physical opening of the projector cover and the transmission request generating circuit operates, based on an detecting operation of the opening detecting switch, to transmit the received beam level transmission request signal to the beam receiving unit. Accordingly, when the beam receiving unit receives the received beam level transmission request signal, the level output circuit transmits the level display signal indicative of the amount of the infrared beam received by the beam receiving unit to the beam projecting unit. Thus, regardless of whether a receiver cover enclosing and projecting circuit components of the beam receiving unit is physically opened, i.e., removed, the servicing worker can perform an accurate axis alignment while looking at the level display signal at the site of installation of the beam projecting unit and, therefore, the workability is high.
In a preferred embodiment of the present invention, the transmission request generating circuit is so designed as to superimpose the received beam level transmission request signal on the infrared beam projected from the beam projecting unit. Accordingly, with no need to provide a communicating means for conducting a communication from the beam projecting unit towards the beam receiving unit, the received beam level transmission request signal can be transmitted from the beam projecting unit towards the beam receiving unit.
In another preferred embodiment of the present invention, the beam receiving unit may include an amplifier for amplifying the infrared beam received by the beam receiving unit, and a received beam level suppressing circuit for controlling the amplifier to reduce the received beam level by a predetermined level corresponding to the amount of the infrared beam attenuated or reduced as it passes through the projector cover of the beam projecting unit. This is particularly advantageous in that since even though the projector cover is physically opened or removed, the amount of the infrared beam received by the beam receiving unit can be displayed by the level meter of the beam projecting unit at the same signal level as the signal level attained when the projector cover is mounted, the alignment of the respective optical axes of the beam projecting and receiving units can accurately be achieved.
It is to be noted that the term xe2x80x9cphysical openingxe2x80x9d used in connection with the projector and receiver cover in the description made hereinabove and hereinafter is intended not only to mean that the cover is removed away from the associated base, but also to mean that the cover is hingedly opened relative to the associated base to which it is hinged and is thus used in the sense that when the cover is opened, internal component parts covered and projected by such cover are rendered open to the outside regardless of whether the cover remains hingedly affixed to the associated base or whether it be separated from the associated base.